acoustics dissertation

8/17/2019 Acoustics Dissertation

1/63

DISSERTATION

ON

“ARCHITECTURAL ACOUSTICS AND ITS

TREATMENT”

Submitted by:

SAIF SIDDIQUI091110025

Under the guidance ofDr. ANUPAMA SHARMA

DEPARTMENT OF ARCHITECTURE AND PLANNING

Maulana Azad National Institute of Technology, Bhopal


2/63

1

APRIL 2013

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY,

BHOPAL DEPARTMENT OF ARCHITECTURE AND PLANNING

DECLARATION

This Dissertation in subject AR 494, entitled “ARCHITECTURAL ACOUSTICS

AND ITS TREATMENT” is being submitted as part of requirement for eighth

semester of Bachelor of Architecture by the undersigned for evaluation.

The matter embodied in this dissertation is either my own work or compilation of

others’ work, acknowledged properly. If, in future, it is found that the above statement

is false, then I have no objection in withdrawal of my Dissertation and any other

action taken by the Institute.

Date:

SAIF SIDDIQUI

091110025


3/63

2

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY,

BHOPAL

DEPARTMENT OF ARCHITECTURE AND PLANNING

CERTIFICATE

This is to certify that the Dissertation entitle “ARCHITECTURAL

ACOUSTICS AND ITS TREATMENT” is a piece of research work done by

Saif Siddiqui under my guidance and supervision and to the best of my

knowledge and belief that this dissertation is:

(i) Embodies the work of the candidate himself;

(ii) has duly been completed;

(iii) Up to the standard both in respect of contents and language for

being referred to the examiner.

Recommended

Dr. Anupama SharmaAssociate Professor,Department of Architecture and PlanningMANIT, Bhopal.Date


4/63

3

ACKNOWLEDGEMENT

I deemed it my privilege to extend my profound gratitude and appreciation to all those

who have directly or indirectly involved themselves in helping me to proceed with the

Dissertation work.

My sincere appreciation and thanks to Supervisor/guide Dr. Anupama Sharma for

their diligent attention towards the dissertation throughout all stages of work. Their

comments and criticism have been invaluable.

I am thankful to all faculty members for their inspiration, without which it was

impossible to finish the task.

The writing of this dissertation has been one of the most significant academic

challenges I have ever taken. Though the following dissertation is an individual work,

I could never have reached the heights or explored the depths without the help of

books published by various authors, the e-books available on the internet and websites

providing information related to my dissertation topic.

SAIF SIDDIQUI

091110025


5/63

4

Table of Content

Declaration ................................................................. Error! Bookmark not defined.

Acknowledgement ...................................................... Error! Bookmark not defined.

Table of Content .................................................................................................... 4

Chapter-1. Synopsis .......................................................................................... 7

1.1 Title ................................................................................................................. 7

1.2 Needs and Concerns ......................................................................................... 8

1.3 Aim ................................................................................................................. 8

1.4 Objectives........................................................................................................ 8

1.5 Scope .............................................................................................................. 8

Chapter-2. Introduction .................................................................................... 9

2.1 Acoustics ...............................................................Error! Bookmark not defined.

2.2 History of Acoustics ....................................................................................... 10

2.3 Sound and its Mechanism .............................................................................. 16

2.4 Noise ..................................................................... Error! Bookmark not defined.

Chapter-3. Acoustical Treatment Of Various Spaces ........................................ 35

3.1 Classrooms .................................................................................................... 35

3.2 Concert Hall ................................................................................................... 36

3.3 Office ............................................................................................................ 38

3.4 Studio ............................................................................................................ 39

3.4 Theatre .......................................................................................................... 40

Chapter-4. Acoustic Materials ........................................................................ 41

Chapter-5. Acoustical Treatments ................................................................... 42

5.1 Common Construction Materials .......................................................................... 42


6/63

5

5.2 Specialtiy Construction Materials ................................................................... 44

5.3 Floors ............................................................................................................ 46

5.4 Stringers ........................................................................................................ 49

5.2 Ceilings .......................................................................................................... 50

5.3 Walls ............................................................................................................. 52

5.4 Doors ............................................................................................................ 54

5.5 Windows ....................................................................................................... 57

Chapter-6. Conclusion .................................................................................... 60

Chapter-7. References ......................................................................................... 60


7/63

6


8/63

7

Chapter-1. Synopsis

1.1 Title

Architectural Acoustics And Its Treatment

1.2 Introduction

Architectural acoustics refers to the control of sound and vibrations within buildings.

Although architectural acoustics was first applied to opera houses and concert halls,

this branch of acoustical engineering applies to any enclosed area, whether concert

halls, office spaces, or ventilation ducts.

The acoustics of rooms are often considered to ensure speech intelligibility and privacy. One thing that can affect speech intelligibility is standing waves. A standing

wave results from a sound wave reflected 180 degrees out of phase with its incident

wave, which often occurs for at least one specific frequency when two walls are

placed parallel to each other. To avoid this, many rooms are designed with angled

walls. A second potential cause of poor speech intelligibility is reverberation. This

effect can be reduced through porous absorbing materials. Examples of these include

glass or mineral fibers, textiles, and polyurethane cell foams. Since the absorption of

each material is different for different frequencies of sound, the materials used often

vary based on the intended purpose of the room, though compound partitions, or

layered combinations of different materials, make more effective absorbers. A third

common technique for room acoustics is the use of masking. Masking is the canceling

or drowning out of other sounds. Although this raises the overall sound pressure,

masking can make irritating noises less distracting and add speech privacy As these

examples highlight, room acoustics are a regular part of architectural design.

Reducing ventilation noise serves as another example of applied architectural

acoustics. Many heating, ventilation, and air conditioning systems have silencers.

Silencers can actively cancel noise by electronic feed forward and feedback

techniques, or muffle the sound by either having sudden changes in cross section or

walls with absorbent linings.Architectural acoustics involves the control of sound for

ventilation, rooms, and anything else indoors.

.

http://en.wikipedia.org/wiki/Reverberationhttp://en.wikipedia.org/wiki/Reverberationhttp://en.wikipedia.org/wiki/Reverberationhttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Reverberation


9/63

8

1.3 Needs and Concerns

In today’s architectural environment, good acoustical design isn’t a luxury – it’s a

necessity. Acoustics impacts everything from employee productivity in office settings

to performance quality in auditoriums to the market value of apartments,

condominiums and single-family homes. While the science behind sound is well

understood, using that science to create desired acoustical performance within a

specific building or room is complex. There’s no single acoustical “solution” that can

be universally applied to building design. Each built environment offers its own

unique set of acoustical parameters. The acoustical design for a business conference

room, for instance, differs greatly from the design needed for a kindergarten

classroom. Understanding these differences and knowing how to utilize building

materials, system design and technologies are key factors behind successful acoustical

design. This research will provide basic background on the science and measurement

of sound, as well as insights into some of the principles of architectural acoustical

design.

1.4 Aim

To study the architectural acoustical designing of spaces.

1.5 Objectives

To study the sound and its mechanism

Study acoustics of an enclosure..

To study treatment of moise..

1.6

ScopeSince this is an architectural report, the literature study will cover study of acoustics

in an architectural space. This research will provide basic background on

Introduction to sound, as well as insights into acoustical designing of spaces

principles and noise reduction techniques.


10/63

9

1.7 Methodology

Literature survey

1. Basics of acoustics

2. Various acoustical treatments

3. Relevant case studies.

study of the acoustical materials for treatments

acoustical measures for respective enclosures.

Chapter-2. Introduction

2.1 Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in

gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist

who works in the field of acoustics is an acoustician while someone working in the field of

acoustics technology may be called an acoustical or audio engineer. The application of

acoustics can be seen in almost all aspects of modern society with the most obvious being the

audio and noise control industries.

The word "acoustic" is derived from the Greek word ακουστικός (akoustikos),

meaning "of or for hearing, ready to hear" and that from ἀκουστός (akoustos), "heard,

audible", which in turn derives from the verb ἀκούω (akouo), "I hear".

The Latin synonym is "sonic", after which the term sonics used to be a synonym for

acoustics and later a branch of acoustics. Frequencies above and below the audible

range are called "ultrasonic" and "infrasonic", respectively.

Figure 3.1 Auditorium Stravinski, Montreux

http://en.wiktionary.org/wiki/%CE%B1%CE%BA%CE%BF%CF%85%CF%83%CF%84%CE%B9%CE%BA%CF%8C%CF%82http://en.wiktionary.org/wiki/%CE%B1%CE%BA%CE%BF%CF%85%CF%83%CF%84%CE%B9%CE%BA%CF%8C%CF%82http://en.wiktionary.org/wiki/%CE%B1%CE%BA%CE%BF%CF%85%CF%83%CF%84%CE%B9%CE%BA%CF%8C%CF%82http://en.wiktionary.org/wiki/%E1%BC%80%CE%BA%CE%BF%CF%8D%CF%89http://en.wiktionary.org/wiki/%E1%BC%80%CE%BA%CE%BF%CF%8D%CF%89http://en.wiktionary.org/wiki/%E1%BC%80%CE%BA%CE%BF%CF%8D%CF%89http://en.wiktionary.org/wiki/%E1%BC%80%CE%BA%CE%BF%CF%8D%CF%89http://en.wiktionary.org/wiki/%CE%B1%CE%BA%CE%BF%CF%85%CF%83%CF%84%CE%B9%CE%BA%CF%8C%CF%82


11/63

10

The acoustical environment of a workspace is typically given little or no attention

during project planning and design. The functionality and aesthetics of the workspace

are usually the primary focus of the designer. Too often overlooked, are the factors

contributing to the productivity of employees occupying the workspace. Providing a

comfortable environment for employees contributes significantly to their optimum

performance and reduced absenteeism. Workspace comfort is really a combination of

factors that includes day lighting and electric lighting, indoor environmental quality,

temperature, and acoustics. The assault on ears in the workplace can come from

traffic noise outside, mechanical equipment in adjacent spaces, and copiers, phones,

and voices within the workspace.

2.2

History of Acoustics

The historical development of architectural acoustics is similar to other fields of

building design, in comprising two parallel strands of ideas – the science and

mathematics of the subject on the one hand, leading to improved understanding of the

phenomena, and the methods used by designers when faced with the challenge of a

new building on the other, especially when the task differs markedly from precedent.

The two nineteenth-century classic works on the physics of acoustics (Helmholz

1863; Strutt 1877-78) hardly mentioned the acoustics of theatres or other rooms, and

the science they contained only began to be used by architectural acousticians in the

mid-twentieth century. While these two branches of knowledge are closely related, it

was not a case of theory leading to practice, or vice versa: the two were symbiotic.

2.2.1 Acoustics in The Ancient World

Vitruvius on acoustics and theatre design

The Roman engineer Vitruvius devoted several chapters of his book on building

design and construction to the location and design of theatres (Vitruvius, Book V). He

advised that they should be located away from winds and from “marshy districts and

other unwholesome quarters” and also on their orientation with respect to the sun and

the surrounding terrain. He addressed key geometric issues such as the plan and

section, sight lines, numbers and locations of entrances and exits, and finally

considered the subject of acoustics. This highly theoretical section was not his own;

he was repeating what he found in various Greek treatises on acoustics from two or

http://www.wbdg.org/design/productive.phphttp://www.wbdg.org/resources/daylighting.phphttp://www.wbdg.org/resources/daylighting.phphttp://www.wbdg.org/design/productive.php


12/63

11

three centuries earlier which, in turn, probably had their origins in Pythagoras who

first developed the subject around 530 BC. Vitruvius dealt with acoustics from several

points of view. First he introduced harmonics – “an obscure and difficult branch of

musical science, especially for those who do not know Greek”. This science explained

the pitch of notes and the intervals between them in the Greek musical scale, as well

as why some combinations of notes are concordant and others discordant. Next

Vitruvius discussed sound in the auditorium – in particular the need for sound of all

pitches to travel from the stage to the ears of every member of the audience by a

direct route, in the manner of waves created by a pebble thrown into water. This led

logically to both raked seating and the semi-circular plan. He advised against vertical

reflective surfaces that would prevent sound reaching the upper tiers of seats since

this particularly impairs the intelligibility of word endings which, in Greek and Latin,

are vital to comprehension. Such reflected waves, he wrote, can also interfere with the

direct waves and distort sounds for the listener. These explanations differ remarkably

little from how we would put it today. Thirdly, Vitruvius explained that the site of a

theatre itself must be carefully selected taking account of acoustics: it must not have

an echo, nor give reflections that can lead to direct (incident) and reflected sounds

interfering.

Vitruvius also discusses the use of sounding vessels – nowadays called Helmholz

resonators, after the nineteenth-century German physicist who explained how they

function – which, he says, reinforce certain frequencies of the human voice and can

increase intelligibility. These open-ended vessels were made of bronze and tuned to

six notes of the chromatic scale. Two sets of six were arranged beneath a tier of seats

symmetrically either side of the centre line of the theatre. If the theatre were

particularly large, two additional sets of vessels should be installed in higher rows,

each a few semi tones lower in pitch – a total of thirty six different notes. Vitruvius

admits he knows of no theatres that had actually been built in Rome with sounding

vessels. The reason, he explains, is that “the many theatres that are constructed in

Rome every year contain a good deal of wood which does not lead to the same

problems with reflections as stone”. Also, he says, the timber panels themselves can

resonate in a manner similar to the air in a sounding vessel and so improve

intelligibility. As to the effectiveness of sounding vessels, they are known today not to

improve intelligibility and that is probably why they were not used in Rome. Whether


13/63

12

the Roman theatres were as good as the Greek ones, we do not know, but there is no

doubt that both were designed with great understanding of acoustics and expertise in

using this understanding to achieve demonstrably better results.

One final recommendation from Vitruvius on acoustics was for a senate house. The

height of a senate house should be half the width of the building, he says, and

coronae, or cornices, made of woodwork or stucco, should be fixed half way up the

inside faces of the walls around the entire room. Without these, he says, the voices of

men engaged in discourse are lost in the high roof. With coronae, the sound of the

voices is ‘detained before rising’ and so is more intelligible to the ear.

Acoustics In The Mediaeval And Renaissance Eras

No significant writings on the acoustics of buildings survive from mediaeval or

Renaissance times (Hunt 1978). Vitruvius was published in the late 15th century and

would have been known by most designers of large buildings. However, it is not

possible to identify precise ways in which his guidance was followed, either in

cathedrals or, from the late Renaissance, in theatres. The development of music from

the 12th century provides evidence of a good understanding of the acoustics of

cathedrals; however, their legendary acoustic qualities are more indebted to the skill

of composers and musicians than to the buildings themselves or their designers. They

have long reverberation times because sound waves are reflected many times with

little loss of intensity which means that musical rhythms have to be slow to be

intelligible, and percussive instruments must not be used to avoid the inevitable

machinegun effect of any echo. The acoustic of the space favours those instruments

with a gradual attack to each note, and which sustain their notes – for example the

organ, flute, violin and the human voice. For speech, however, the long reverberation

time is a disaster. As the distance between speaker and listener increases, so the sound

reaching the ear directly is increasingly swamped by the reflected sounds arriving by

indirect, longer sound paths. Speech is thus generally unintelligible at any distance

greater than a few meters, which phenomenon has an interesting architectural effect.

Since it is the longer wavelengths of lower notes that are more effectively reflected,

people talking in cathedrals are naturally and unconsciously inclined to whisper,

irrespective of any reverence for the religious nature of the buildings they may feel,

because whispering removes the lower frequencies of the human voice.


14/63

13

Early Modern Design Guidance – Eighteenth Century

As in the ancient world of building described by Vitruvius, it was the intelligibility of

speech that drew the attention of 17th and 18th century building designers to the

acoustic performance of building interiors, especially in two types of building –

theatres and the debating chambers used by politicians. During the eighteenth century

the importance of room acoustics was further heightened with the invention of a

number of musical instruments such as the harpsichord and fortepiano, and the

growing popularity, in elite circles at least, of chamber music. The new instruments

used ingenious mechanisms and large sounding boards to produce plucked and

percussive notes with unprecedented speed and at much greater volumes than earlier

instruments such as the lute, harp and clavichord. When played in a room with a very

live acoustic, the individual notes became indistinguishable and the objectives of the

instrument makers and musicians were ruined.

Throughout Europe the second half of the eighteenth century saw a boom in theatre

building in the major cities, and designers generally learned from the acoustic

disasters of the early century. By the late eighteenth century it was common practice

to use the ceiling or soffit above the front of the stage as a ‘sounding board’ (actually

a reflector) and the ceiling over the orchestra pit to ‘throw the voice forward’ from the

stage to the back of the stalls and to the galleries. The first design guides for theatres

discussed acoustics alongside the equally important issue of line-of-sight (Patte 1782,

Saunders 1790, Rhode 1800, Langhans 1810). These and others followed Patte’s

example in showing ray diagrams to visualise sound paths.

Fig. 3.2 Ray diagrams for different theatre plans; (Patte 1782, Plate 1)


15/63

14

Wallace Clement Sabine – “Father Of Architectural Acoustics”

The man who has no rival in being called “the father of architectural acoustics” was

Wallace Clement Sabine (1868-1919) (Sabine 1922; Beyer 1999, pp.186-191;

Thompson 1992, 2002). Sabine was a lecturer in physics in the department of natural

philosophy at Harvard University and was approached in 1895 to advise on how to

improve the poor acoustics of a new lecture theatre in the University’s Fogg Art

Museum. This lecture theatre had been designed to emulate a classical Greek theatre

and followed the same principles of acoustic design that Vitruvius had written down.

These addressed the need of intelligibility by focusing mainly on maintaining the

volume of the direct sound that reached the listener’s ear. The speaker was placed

above the level of the front row of the audience; the seating was raked upwardstowards back of the auditorium; and a wall was placed behind the speaker to reflect

sound into the auditorium. However, such principles were intended for open-air

theatres and took no account of sound reflected from walls or the roof. In an enclosed

room these reflected sounds also reach the listener’s ear and, since there will be many

sounds, arriving at different times, the result is confusion with direct sound from a

speaker competing with reflections of earlier sounds. Sabine realised this was how

intelligibility was lost, like many before him. Being a physicist, however, hisapproach was to conduct experiments to measure how the loudness of the reflections

was influenced by the reflecting surfaces in the lecture theatre. His aim was to

discover the relationship between the dimensions of the room and the rate at which a

sound became quieter and eventually became inaudible. He called this rate of decay

the reverberation time and defined it as the time, in seconds, for a sound to decay to

one millionth of its original loudness (a fall of 60dB). Sabine had to work at night to

ensure all extraneous sounds were avoided. He used a single organ pipe with a

frequency of 512 Herz (an octave above middle C). In 1895 there were no

microphones or audio-electronics Proceedings of the Third International Congress on

Construction History, May 2009 and the judgement as to when the sound was

inaudible was made by the experimenter himself. An electric chronograph recorded

the times to one-hundredth of a second. By covering more and more of the

auditorium’s wooden seats with soft cushions, he showed that the reverberation time

was inversely proportional to the number of seats covered with cushions. He repeated

the experiments in eleven other rooms in the university, with volumes ranging from a


16/63

15

lecture theatre of 9300 cubic metres down to an office of just 35 cubic metres. From

the results he derived the equation for which his name is well-known giving the

relationship between the reverberation time (RT), of a room, in seconds, its volume

(V), in cubic metres, and the area (A), in square metres, of sound-absorbing surfaces

in the room. (1) Sabine used this equation to give an objective means of comparing

different auditoria and, in particular, to compare the proposed design for the new

Boston Music Hall with the Leipzig Gewandhaus, on which its overall shape was

based, and the old Music Hall in Boston. He was able to specify, for the first time, the

precise degree of sound absorption in the interior of the new Boston hall needed to

achieve the same reverberation time as the Leipzig Gewandhaus whose seating

capacity it exceeded by 70%, and volume by 40%. Sabine’s predictions were accurate

and the acoustic of the new hall was widely praised. He had fulfilled his goal of

overcoming the “unwarranted mysticism” that then surrounded the subject of

architectural acoustics and, most importantly, achieved “the calculation of

reverberation in advance of construction”. Sabine was soon being approached by the

owners of various types of room to advise on how to rectify their acoustic problems.

Often this followed the failed attempts by others to deal with the problems. Sabine

noted the persistent use of a traditional but wholly ineffective remedy which involved

stretching a grid of steel wires in the top of a church, theatre or court room which

suffered too much reverberation on the mistaken believe that the wires would resonate

and absorb sound. In New York and Boston he had seen theatres and churches with

just four or five wires stretched across the room while in other auditoria several miles

of wire had been used, all without the slightest effect. As part of his diagnosis of

acoustic problems he would sometimes plot a contour map showing the distribution of

the sound intensity. This helped him identify the source of the worst sound reflections

from the walls and ceiling and hence reduce them by using sound-absorbing panels or

adding decorations that would break up strong reflections from large plane surfaces.

Sabine also turned his attention to the design of new theatres and how best to create a

near-uniform acoustic experience for every member of the audience. To help him in

these studies he used the newly-perfected

schlieren method of photography to show sound waves passing through air in two-

dimensional models of auditoria (Fig.2). He was thus able to show in plan and


17/63

16

section, how sound waves were reflected and broken up as they emanated from the

stage into the auditorium. Outside the field of building structures this was probably

the first use of a scale model to investigate the engineering behaviour of a building.

Fig 3.3 Photographs showing the progress of sound waves through a model of a theatre.

The development of design methods for the acoustics of auditoria has followed the

same pattern observed in other branches of building engineering design. Initially

designers used their own experience to observe and improve their art and collected

their experience in the form of simple design rules which could be passed on to other

designers. In acoustics this approach was known in ancient times and has continued

even into the twentieth century. The technical difficulty of measuring acoustic

phenomena delayed a truly scientific approach to understanding acoustics until the

late eighteenth century (over a century later than for structural engineering). The firstscientific concept in acoustics, defined in quantitative terms by Sabine in the 1890s,

was the reverberation time whose relationship to the dimensions of a room was

expressed as an empirical quantity known as the absorptivity of the surfaces of the

room. This approach remains the most important in acoustic design today. The testing

of scale models together with the use of non-dimensional constants was developed in

acoustics simultaneously with their use in the design of building structures, first in the

1930s and more widely in the 1960s. Their use consolidated the understanding of

acoustic phenomena and laid the foundation for creating mathematical models using

computers.

2.3 Sound and its Mechanism

Sound is a mechanical wave that is an oscillation of pressure transmitted through

a solid, liquid, or gas, composed of frequencies within the range of hearing. Sound

also travels through plasma


18/63

17

2.3.1 Propagation of sound

Sound is a sequence of waves of pressure that propagates through compressible media

such as air or water. (Sound can propagate through solids as well, but there are

additional modes of propagation). Sound that is perceptible by humans has

frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm.

During propagation, waves can be reflected, refracted, or attenuated by the medium.

Fig. 3.2 Travelling of sound waves

The behaviour of sound propagation is generally affected by three things:

A relationship between density and pressure. This relationship, affected by

temperature, determines the speed of sound within the medium.

The propagation is also affected by the motion of the medium itself. For

example, sound moving through wind. Independent of the motion of sound

through the medium, if the medium is moving, the sound is further transported.

The viscosity of the medium also affects the motion of sound waves. It

determines the rate at which sound is attenuated. For many media, such as air or

water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical

properties, it may be refracted (either dispersed or focused).

2.3.2 Perception of Sound

The perception of sound in any organism is limited to a certain range of frequencies.

For humans, hearing is normally limited to frequencies between about 20 Hzand

20,000 Hz (20 kHz),[3] although these limits are not definite. The upper limit generally

decreases with age. Other species have a different range of hearing. For example,

http://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/KHzhttp://en.wikipedia.org/wiki/Sound#cite_note-3http://en.wikipedia.org/wiki/Sound#cite_note-3http://en.wikipedia.org/wiki/Sound#cite_note-3http://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Sound#cite_note-3http://en.wikipedia.org/wiki/KHzhttp://en.wikipedia.org/wiki/Hertz


19/63

18

dogs can perceive vibrations higher than 20 kHz, but are deaf to anything below

40 Hz. As a signal perceived by one of the major senses, sound is used by many

species for detecting danger, navigation, predation, and communication. Earth's

atmosphere, water, and virtually any physical phenomenon, such as fire,

rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds.

Many species, such as frogs, birds, marine and terrestrial mammals, have also

developed special organs to produce sound. In some species, these

produce song and speech. Furthermore, humans have developed culture and

technology (such as music, telephone and radio) that allows them to generate, record,

transmit, and broadcast sound. The scientific study of human sound perception is

known as psychoacoustics.

2.3.3 Physics of Sound

The mechanical vibrations that can be interpreted as sound are able to travel through

all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the

sound is called the medium. Sound cannot travel through a vacuum.

Longitudinal and transverse waves

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also

called compression waves. Through solids, however, it can be transmitted as both

longitudinal waves and transverse waves. Longitudinal sound waves are waves of

alternating pressure deviations from the equilibrium pressure, causing local regions

of compression and rarefaction, while transverse waves (in solids) are waves of

alternating shear stress at right angle to the direction of propagation.

Matter in the medium is periodically displaced by a sound wave, and thus oscillates.

The energy carried by the sound wave converts back and forth between the potentialenergy of the extra compression (in case of longitudinal waves) or lateral

displacement strain (in case of transverse waves) of the matter and the kinetic energy

of the oscillations of the medium.

Sound wave properties and characteristics

http://en.wikipedia.org/wiki/Sensehttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Windhttp://en.wikipedia.org/wiki/Ocean_surface_wavehttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Froghttp://en.wikipedia.org/wiki/Birdhttp://en.wikipedia.org/wiki/Marine_mammalshttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Organ_(anatomy)http://en.wikipedia.org/wiki/Bird_vocalizationhttp://en.wikipedia.org/wiki/Speech_communicationhttp://en.wikipedia.org/wiki/Humanhttp://en.wikipedia.org/wiki/Musichttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Psychoacousticshttp://en.wikipedia.org/wiki/Psychoacousticshttp://en.wikipedia.org/wiki/State_of_matterhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Plasma_(physics)http://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Longitudinal_wavehttp://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Mechanical_equilibriumhttp://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Rarefactionhttp://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Rarefactionhttp://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Mechanical_equilibriumhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Compression_(physical)http://en.wikipedia.org/wiki/Longitudinal_wavehttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Plasma_(physics)http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/State_of_matterhttp://en.wikipedia.org/wiki/Psychoacousticshttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Musichttp://en.wikipedia.org/wiki/Humanhttp://en.wikipedia.org/wiki/Speech_communicationhttp://en.wikipedia.org/wiki/Bird_vocalizationhttp://en.wikipedia.org/wiki/Organ_(anatomy)http://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Marine_mammalshttp://en.wikipedia.org/wiki/Birdhttp://en.wikipedia.org/wiki/Froghttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Ocean_surface_wavehttp://en.wikipedia.org/wiki/Windhttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Sense


20/63

19

Figure 3.3 Sinusoidal waves of various frequencies; the bottom waves have higher frequencies

than those above. The horizontal axis represents time.

Sound waves are often simplified to a description in terms of sinusoidal plane waves,

which are characterized by these generic properties:

Frequency, or its inverse, the period

Wavelength

Wave number

Amplitude Sound pressure

Sound intensity

Speed of sound

Direction

Sometimes speed and direction is combined as a velocity vector; wave number and

direction are combined as a wave vector.

Transverse waves, also known as shear waves, have the additional

property, polarization, and are not a characteristic of sound waves.

2.3.4

Speed of Sound

The speed of sound depends on the medium the waves pass through, and is a

fundamental property of the material. In general, the speed of sound is proportional to

the square root of the ratio of the elastic modulus (stiffness) of the medium to

its density. Those physical properties and the speed of sound change with ambient

conditions. For example, the speed of sound in gases depends on temperature. In

20 °C (68 °F) air at sea level, the speed of sound is approximately 343 m/s

(1,230 km/h; 767 mph) using the formula "v = (331 + 0.6 T) m/s". In fresh water, also

at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph).

In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).[6] The

speed of sound is also slightly sensitive (a second-order anharmonic effect) to the

sound amplitude, which means that there are nonlinear propagation effects, such as

the production of harmonics and mixed tones not present in the original sound.

http://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Wavenumberhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Sound_intensityhttp://en.wikipedia.org/wiki/Speed_of_soundhttp://en.wikipedia.org/wiki/Direction_(geometry,_geography)http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Vector_(geometric)http://en.wikipedia.org/wiki/Wave_vectorhttp://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Square_roothttp://en.wikipedia.org/wiki/Ratiohttp://en.wikipedia.org/wiki/Elastic_modulushttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Sea_levelhttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Sound#cite_note-6http://en.wikipedia.org/wiki/Sound#cite_note-6http://en.wikipedia.org/wiki/Sound#cite_note-6http://en.wikipedia.org/wiki/Anharmonicityhttp://en.wikipedia.org/wiki/Anharmonicityhttp://en.wikipedia.org/wiki/Sound#cite_note-6http://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Sea_levelhttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Elastic_modulushttp://en.wikipedia.org/wiki/Ratiohttp://en.wikipedia.org/wiki/Square_roothttp://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Transverse_wavehttp://en.wikipedia.org/wiki/Wave_vectorhttp://en.wikipedia.org/wiki/Vector_(geometric)http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Direction_(geometry,_geography)http://en.wikipedia.org/wiki/Speed_of_soundhttp://en.wikipedia.org/wiki/Sound_intensityhttp://en.wikipedia.org/wiki/Sound_pressurehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Wavenumberhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Sine_wave


21/63

20

2.3.5 Measurement of Sound

Sound is measured in dB (decibels). The decibel (dB) is a logarithmic unit that

indicates the ratio of a physical quantity (usually power or intensity) relative to a

specified or implied reference level. A ratio in decibels is ten times the logarithm to

base 10 of the ratio of two power quantities.[1] A decibel is one tenth of a bel, a

seldom-used unit named in honor of Alexander Graham Bell.

Fig. 3.4 Various sounds and their dB units.

2.3.6 Acoustic Terms

Reverberation

enclosed space, when a sound source stops emitting

it takes some time for the sound to become inaudible. This prolongation of the so

http://en.wikipedia.org/wiki/Logarithmic_unithttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Intensity_(physics)http://en.wikipedia.org/wiki/Common_logarithmhttp://en.wikipedia.org/wiki/Common_logarithmhttp://en.wikipedia.org/wiki/Decibel#cite_note-1http://en.wikipedia.org/wiki/Decibel#cite_note-1http://en.wikipedia.org/wiki/Decibel#cite_note-1http://en.wikipedia.org/wiki/Alexander_Graham_Bellhttp://en.wikipedia.org/wiki/Alexander_Graham_Bellhttp://en.wikipedia.org/wiki/Alexander_Graham_Bellhttp://en.wikipedia.org/wiki/Decibel#cite_note-1http://en.wikipedia.org/wiki/Common_logarithmhttp://en.wikipedia.org/wiki/Common_logarithmhttp://en.wikipedia.org/wiki/Intensity_(physics)http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Logarithmic_unit


22/63

21

room caused by continued multiple reflections is called reverberation. Re

time plays a crucial role in the quality of music and the ability to understand s

given space. When room surfaces are highly reflective, sound continues to

reverberate. The effect of this condition is described as a live space with a long rev

time. A high reverberation time will cause a build-up of the noise level in a space.

of reverberation time on a given space are crucial to musical conditions and und

speech. It is difficult to choose an optimum reverberation time in a multi-functio

different uses require different reverberation times. A reverberation time that is op

a music program could be disastrous to the intelligibility of the spoken word. Co

reverberation time that is excellent for speech can cause music to sound dry and fla

Reflections

Reflected sound strikes a surface or several surfaces before reacreceiver. These reflections can have unwanted or evenconsequences. Although reverberation is due to continuedreflections, controlling the Reverberation Time in a space does notspace will be free from problems from r

Reflective corners or peaked ceilings can create a “megaphone” effect potentiall

annoying reflections and loud spaces. Reflective parallel surfaces lend themselves t

acoustical problem called standing waves, creating a “fluttering” of sound betweesurfaces.

Reflections can be attributed to the shape of the space as well as the material on thDomes and concave surfaces cause reflections to be focused rather than dispersedcause annoying sound reflections. Absorptive surface treatments can help to elimreverberation and reflection problems.

Noise Reduction Coefficient

The Noise Reduction Coefficient (NRC) is a single-number index for rating how ab

particular material is. Although the standard is often abused, it is simply the average ofrequency sound absorption coefficients (250, 500, 1000 and 2000 Hertz rounded to t5%). The NRC gives no information as to how absorptive a material is in the lofrequencies, nor does it have anything to do with the material’s barrier effect.

Sound Transmission Class (STC):

The Sound Transmission Class (STC) is a single-number rating of amaterial’s or assembly’s barrier effect. Higher STC values are more

efficient for reducing sound transmission. For example, loud speech can

be understood fairly well through an STC 30 wall but should not beaudible through an STC 60 wall. The rating assesses the airborne

http://www.acoustics.com/reverberation.asphttp://www.acoustics.com/reverberation.asphttp://www.acoustics.com/nrc.asphttp://www.acoustics.com/stc.asphttp://www.acoustics.com/stc.asphttp://www.acoustics.com/nrc.asphttp://www.acoustics.com/reverberation.asphttp://www.acoustics.com/reverberation.asp


23/63

22

sound transmission performance at a range of frequencies from 125 Hertz to 4000Hertz. This range is consistent with the frequency range of speech. The STC ratingdoes not assess the low frequency sound transfer. Special consideration must be givento spaces where the noise transfer concern is other than speech, such as mechanicalequipment or music.

Even with a high STC rating, any penetration, air-gap, or “flanking” path can seriouslydegrade the isolation quality of a wall. Flanking paths are the means for sound totransfer from one space to another other than through the wall. Sound can flank over,under, or around a wall. Sound can also travel through common ductwork, plumbingor corridors.

2.4 Noise

Fig 3.5 graph showing noise levels

In relation to sound, noise is not necessarily random. Sounds, particularly loud ones, that

disturb people or make it difficult to hear wanted sounds, are noise. For example,

conversations of other people may be called noise by people not involved in any of them;

any unwanted sound such as domesticated dogs barking, neighbours playing loud music,

portable mechanical saws, road traffic sounds, or a distant aircraft in quiet countryside, is

called noise.

Acoustic noise can be anything from quiet but annoying to loud and harmful. At one

extreme users of public transport sometimes complain about the faint and tinny sounds

emanating from the headphones or earbuds of somebody listening to a portable audio

player; at the other the sound of very loud music, a jet engine at close quarters, etc. can

cause permanent irreversible hearing damage.

Sound intensity follows an inverse square law with distance from the source; doubling thedistance from a noise source reduces its intensity by a factor of four, or 6 dB.

http://en.wikipedia.org/wiki/Public_transporthttp://en.wikipedia.org/wiki/Earbudhttp://en.wikipedia.org/wiki/Portable_audio_playerhttp://en.wikipedia.org/wiki/Portable_audio_playerhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Sound_intensityhttp://en.wikipedia.org/wiki/Inverse_square_law#Acousticshttp://en.wikipedia.org/wiki/Inverse_square_law#Acousticshttp://en.wikipedia.org/wiki/Sound_intensityhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Portable_audio_playerhttp://en.wikipedia.org/wiki/Portable_audio_playerhttp://en.wikipedia.org/wiki/Earbudhttp://en.wikipedia.org/wiki/Public_transport


24/63

23

2.4.1 Reverberation time

With this theory described, the reverberation time can be defined. It is the time for the

level of energy to decrease of 60 dB. It depends on the volume of the room V and the

equivalent

absorption area a :T60 =0.16V

a Sabine formula

This reverberation time is the fundamental parameter in room acoustics and depends

trough the equivalent absorption area and the absorption coefficients on the frequency. It

is used for several measurement :

• Measurement of an absorption coefficient of a material

• Measurement of the power of a source

• Measurement of the transmission of a wall

2.4.2 Controlling Noise

Controlling Noise Between Spaces

Controlling noise between spaces is frequently an issue in residential projects and office spaces. Noise will travel between spaces at the weakest

points, such as through a door or outlet. There is no reason to spend money or effort toimprove the walls until all the weak points are controlled.

General rules of thumb for controlling noise between spaces:

A wall must extend to the structural deck in order to achieve optimal isolation.Walls extending only to a dropped ceiling will result in inadequate isolation.

Sound will travel through the weakest structural elements, which, many times, arethe doors or electrical outlets. When the mass of a barrier is doubled, the isolation quality (or STC rating)

increases by five, which is clearly noticeable. Installing insulation within a wall or floor/ceiling cavity will improve the STC

rating by about 4-6 dB, which is clearly noticeable. Often times, specialty insulations do not perform any better than standard batt

insulation. Metal studs perform better than wood studs. Staggering the studs or using dual

studs can provide a substantial increase in isolation. Increasing air space in a wall or window assembly will improve isolation.

Case Study


25/63

24

Location: Newspaper office building

Area of concern: Space between CEO office and boardroom

Additional information: Noise usually travels through spaces at several different points.

Controlling only one point is like trying to save a sinking boat by patching only one holewhen 10 holes exist. You must be thorough to ensure effective results.

Questions to ask client:

Please describe the problem. Does the wall go all the way up to the deck and is it sealed airtight? Does it just go

up to the dropped ceiling? Are there any penetrations through the wall? Are there any penetrations through the wall? Could the noise be going around the wall? Are there any air gaps? Under the door?

At the perimeter of the wall? At the window mullion? Etc?

What materials are used in the space(s)? What are your confidentiality needs?

Client feedback:

The CEO is distracted by noise from the boardroom when there are meetings in progress. There are also confidentiality issues.

The wall does not go up to the deck, it ends at the dropped ceiling. There are no penetrations other than the door. The noise could be going around the wall by means of the door. The materials used in this space are carpet, painted drywall and acoustic tile on the

ceiling. There are two return air ducts about two feet apart, separated only by thewall.

Confidentiality is an issue to some degree, but not a security problem.

Evaluation: In this particular project, there was a door and a window between the two

spaces and the ceiling did not go up to the deck. To improve the acoustics, an

upgraded sealer was added to the doors and a flexible, vinyl barrier was placed on top

of the ceiling above the two spaces (since the wall could not be extended to the deck).

Creating a completely confidential space is very difficult and extremely expensive.

Since confidentiality was an issue, but not a security matter, this improvement proved

successful.

If further improvements were needed, the next step would be to install a sound

masking system.

Further comments: In another office space, where complete confidentiality was


26/63

25

essential, a very expensive door was installed. This door had an STC rating of 65, but

the surrounding walls had an STC rating of 50. In this case, the walls served as the

weakest point, rather than the door. It’s important to note that the isolation quality of

an assembly is dictated by the weakest element of the assembly.

Controlling Noise from the Outside

When noise from the outside is a distraction, the windows are

often to blame. Exterior walls will typically block at least

between 45 to 50 dB of sound, but even a very high quality window might not even

block 40 dB. When possible, controlling noise at the source is usually the best solution.

Sometimes a barrier can be built around the noise source. Other times, the noise source

can be relocated.

General rules of thumb for controlling noise from the outside:

Typically, the noise transfer will go through the weakest structural element, such

as the door, window or ventilation duct.

When applicable, it is best to control exterior noise at the source.

The isolation provided by a door is only as good as the extent to which it is sealed.

If air can get around or under the door, so can sound.

The majority of exterior noise enters through the windows. Dual-pane windows

with increased air space can improve isolation.

If the noise cannot be reduced to a satisfactory level, consider trying to mask the

annoying noise with a more pleasant noise such as a water feature.

Case Study

Location: Private residence

Area of concern: A neighbor’s pool motor created an annoying hum that could be heard in

the master bedroom.

http://www.acoustics.com/101.asphttp://www.acoustics.com/101.asp


27/63

26

Additional information: In this case, the first thing to do is to check the weakest points,

such as windows and doors. Windows can be replaced with upgraded varieties, or

acoustical inserts can be added for further control. Originally, acoustic absorption was

mistakenly added to the inside of the room. This actually made the problem worse.

Although the noise level within the room decreased, the absorption did nothing to reduce

the exterior noise.


Describe the problem.

What is the noise source?

Where does the noise seem to be coming from? Under the door? Through the

window? Through the ceiling? Etc.?

What changes have already been made?

Ideally, what improvements would you like to see?

Client feedback:

An annoying hum is heard in the master bedroom. It interrupts sleep and interferes

with other activities such as watching television and reading.

The noise is coming from the motor from the neighbor’s pool pump.

The windows are upgraded and an acoustic sealant has been applied to the doors.

Ideally, the noise would be inaudible, or at least not distracting.

Evaluation: In this situation, encapsulating the noise source was the best solution.

Vibration dampening was also used to control the noise. This solution completely met the

client's needs. Additional comments: There are certain noises that are difficult to control at

the source, such as traffic noise. In such cases, look to control the noise at the path by

erecting a barrier, such as a wall. Vegetation provides little, if any, noise reduction. If air

can pass through, so can sound.

Controlling Noise Within a Space

When controlling noise within a space, there are usually two main problems to remedy:a noisy space due to reverberation or a noisy space due to equipment noise.

http://www.trafficnoise.org/http://www.acoustics.com/101.asphttp://www.acoustics.com/101.asphttp://www.trafficnoise.org/


28/63

27

General rules of thumb for controlling noise within a space:

You have to at least double the absorption in a space before there is a noticeable

difference. Every time you double the absorption, the reverberant noise field is

reduced by 3 dB, which is classified as “just perceptible.”

Adding absorption to a space can provide a clearly noticeable improvement if the

space is fairly reverberant to begin with. The practical limit for noise reduction

from absorption is 10 dB, which sounds half as loud.

The improvement will not be as noticeable as you get closer to the noise source.

Carpet is not a cure-all. In fact, it is typically only 15-20% absorptive. It would

take four times as much carpet to have the same impact as a typical acoustic

material, which is about 80% absorptive.

Case Study 1

Location: Retirement Village

Area of concern: Multi-purpose clubhouse

Additional information: The original thought was that the sound system needed to be

upgraded or fixed because it wasn’t “working” properly. Further review showed that it

was the lack of absorption in the room, not the sound system that was causing the

problems.

Questions asked of client:

Please describe the problem.

What are the dimensions of the space?

What activities take place in this room?

Is there a noise issue? A sound system issue? A reverberation ("echo") problem?

When is it the loudest?

Is it difficult to hear someone speaking when there is no loud noise?

Do presenters on stage complain about reflections?


29/63

28

Please describe the ceiling. Is it domed? Peaked? Flat?

What materials are used in this room? Drywall? Wood? Carpet? Tile?

Client feedback:

The room is too loud whenever there is a group in it, especially during dinners.

It’s difficult to hear presenters and understand announcements. Small group

conversations are hindered by excessive surrounding noise.

The space is 65'L x 54'W x 18'H.

The room is used for large dinners, performances, presentations, and other group

activities.

The or iginal assumption was that the problem was the sound system, but we don’thave problems hearing announcements when the room is quiet. It must be a noise

issue within the room itself.

It’s the loudest during dinner when everyone is talking at once.

It is not difficult to hear a presenter when there is no other noise.

Presenters on stage do complain about reflections.

The ceiling is flat drywall.

Drywall and carpet are used throughout the room. Draperies and curtains are used

on the stage.

Evaluation: After speaking with the client and visiting the site, it was obvious that a lack

of absorption was causing the excessive noise in the room. Frequently, in a situation such

as this, a reflective ceiling, which is a large area that will project noise back down to the

floor, causes a majority of problems.

Addressing the ceiling alone would improve the noise level, but would not protect

performers from the problematic reflections called slap-back*. There are a variety of

products available for such applications. The products you choose are dependent upon the

look and feel of the room and your budget. In this case, acoustics improved as a result of

adding material to the ceiling (to control the overall noise) and acoustic wall paneling to

the back wall (to control slap-back and the overall reverberation time).

*Slap- back = A reflective back wall will reflect, or “slap,” the noise back to the source

causing a delay.


30/63

29

Case Study 2

Location: Headquarters for a large credit card company

Area of concern: Credit card processing center

Additional information: The first step in solving a problem related to equipment noise is to

call the manufacturer. Sometimes there is a problem in the installation or in the equipment

operation. Certain pieces of equipment have a retrofit noise reduction kit that can be

purchased to reduce problems.


Please describe the problem.

What are the dimensions of the space?

What activities take place in this room?

Is there a noise issue? A sound system issue? A reverberation ("echo") problem?

When is it the loudest?

Is it difficult to hear someone speaking when there is no loud noise?

Please describe the ceiling. Is it domed? Peaked? Flat?

What materials are used in this room? Drywall? Wood? Carpet? Tile?

Client feedback:

The processing center houses equipment that generates noise at 85-90 dB.

Workers are annoyed by this noise and the company is on the borderline of an

OSHA violation.

The space in question is 260'L x 90'W x 20'H. This room facilitates automated printing and folding of statements and stuffing

envelopes.

Equipment noise is the primary problem.

It is the loudest when all of the equipment is operating, which is during business

hours.

There are no communication issues when the equipment is not running.

Evaluation: It is always best to control noise at the source, which, in this case, is


31/63

30

the equipment itself. The level of improvement is related to the reverberance of the space.

The more reverberant a space is, the more dramatic the possible improvement. For this

project, the space was not too reverberant, so the improvement would not be remarkable,

but it would be noticeable. Hanging vinyl-covered acoustic baffles from the ceiling,

particularly the areas directly above the equipment, controlled the noise from emanating

within the space, but did not reduce the noise level for the equipment operator (though it

did help the other operators).

If adding absorption does not provide enough noise control, it might be necessary to

isolate the noisy areas from the quieter areas. Doing so would result in the implementation

of a hearing protection program for those employees working in the unavoidably louder

areas. In this case, enclosing the equipment with an acoustic shield (of plexi-glass)reduced the noise level for the operator by about 10 dB. The combination of the absorptive

material and the acoustic shield reduced the overall noise by about 4 dB for all employees

in the area, which met the client’s needs and br ought them into OSHA compliance.

Controlling Outside Noise

In certain situations, an outside space must be protected from the

surrounding outside noise. Encapsulation, barriers, increased distance or masking

source are some possible

General rules of thumb for controlling outside noise:

By doubling the distance from a noise source, the level is reduced by 6 dB

noticeable amount. The reduction will not be experienced to this extent with a lisuch as a railroad or freeway (the reduction is around

4-1/2 dB).

A barrier must block the line-of-sight between the source and the receiver in

effective.

You will typically not need a barrier with a surface weight/density greater

pounds/square foot, as long as there are no openings in the wall.

It is difficult to reduce the noise by more than 10 dB with a barrier wall.

Noise barriers can be solid walls, berms or a combination of the two.


32/63

31

The noise wall must be continuous with no openings to be effective. If ai

through the wall, so will sound.

Vegetation, such as trees and bushes, provides very little, if any, noise reduction

Case Study

Location:

Area of concern: A column burial area with a meanderi

Additional information: This space needed to facilitate a solemn and contemplative set

minimizing distractions from a nearby street. Originally, a concrete block wall was usresults were not


Describe the problem.

Describe the ambient noise conditions.

Are there any existing barriers?

What is the desired result?

Client feedback:

The cemetery is next to a relatively busy road. The traffic noise is distracting

who expect a quiet, intimate setting.

Aside from the traffic noise, there are no other major noise sources in the area.

A concrete block wall was used, but the results were not sufficient.

The desired result is a relaxed, meditative atmosphere that is aesthetically cons

the rest of the space.

Evaluation: Since it was not feasible to increase the barrier wall height, a sound

masking system (that is typically used in an office environment) was implemented in

this case. To blend in with the atmosphere, rock speakers that generated pink noise

were placed along the meandering path. Water features served as additional

atmosphere enhancers, and helped to make the masking system sound more natural.

http://www.trafficnoise.org/http://www.trafficnoise.org/http://www.trafficnoise.org/http://www.trafficnoise.org/


33/63

32

These fountains also eliminated hot and cold zones and created a consistent noise

through the entire space. Water features alone would only work when a visitor was

standing directly next to the water.

Additional comments: In many cases, the best outdoor solution is a barrier wall.

Other solutions include encapsulating a noise source (such as an emergency

generator) and adding distance between the receiver and the noise source.

2.4.3 Noise Standrards

Noise Isolation Class (NIC)

Test: NIC is a method for rating a partition's ability to block airborne noise

transfer.

RelatedCode: UBC/IBC and STC

General Information: Similar to a field STC test, NIC is often specified on certain

projects (such as spaces with operable walls, hotels, education facilities). For a

field STC test, the individual transmission loss measurements are modified based

on the reverberation time, the size of the room and the size of the test partition. The

NIC does not include these modifications and simply measures he Transmission

Loss between125and4,000Hz.

Strength: Tests the isolation performance of the assembly in the field. It is good

include an NIC performance requirement within your spec for operable and demounta

walls.

Weakness: The NIC rating is highly dependent on the field conditions of the tested spa

Because of this, the tested rating might not be achieved in other spaces or projects.

Noise Criteria (NC)

Code: This industry standard (also an ANSI standard) usually pertains to HVAC or

mechanical noise impact.

http://www.acoustics.com/universal.asphttp://www.acoustics.com/stc.asphttp://www.acoustics.com/stc.asphttp://www.acoustics.com/universal.asp


34/63

33

Enforcement: This standard is often required for certain certifications (such as

government medical facilities) or included in client specifications/standards (for

example, some companies have NC standards that their buildings must meet).

General Information: An NC level is a standard that describes the relative loudness

of a space, examining a range of frequencies (rather than simply recording the decibel

level). This level illustrates the extent to which noise interferes with speech

intelligibility. NC should be considered for any project where excessive noise would be

irritating to the users, especially where speech intelligibility is important. There are a

few spaces where speech intelligibility is absolutely crucial, including:

Recording studios

Lecture halls

Performance halls

Courtrooms

Libraries

Worship centers

Educational facilities

For some areas, such as machine shops or kitchens, it is not essential to maintain a

particularly low NC level.

NC Level Strength: It is important for design professionals to specify NC ratings to

protect their designs (within reason – specifying an acceptable NC level does not have

to be a burden on the budget). Doing so speaks to your reputation as a responsible

architect or designer and limits your liability.

NC Level Weakness: NC does not account for sound at very low frequencies. In spite

of numerous efforts to establish a widely accepted, useful, single-number rating

method for evaluating noise in a structure, a variety of techniques exist today. The vast

majority of acoustic professionals use the NC standard, but it is still important to be

aware of the other acceptable methods that do account for low frequency levels,

including (but not limited to):


35/63

34

Room Criteria (RC) measures background sound in a building over the

frequency range 16 Hz to 4000 Hz. This rating system requires two steps:

determining the mid-frequency average level and determining the perceived

balance between high and low frequency sound. To view the recommended

ANSI levels for room criteria for various activity areas, click here.

Balanced Noise Criteria (NCB) is based on the ANSI threshold of audibility

pure-tones and is defined as the range of audibility for continuous sound i

specified field from 16 Hz to 8000 Hz.

Sound Transmission Clas (STC)Code: STC rates a partition's or material's ability to block airborne sound.

Enforcement: Appendix Chapter 35 of the ’88 and ’91 UBC, Appendix Chapter 12,Division II of the ’94 and ’97 UBC will be contained in the forthcoming IBC.Although not all municipalities have adopted this appendix chapter, it is stillrecognized as an industry standard.

General Information: The Uniform Building Code (UBC) contains requirements forsound isolation for dwelling units in Group-R occupancies (including hotels, motels,apartments, condominiums, monasteries and convents).

UBC requirements for walls: STC rating of 50 (if tested in a laboratory) or 45 (if testedin the field*).

UBC requirements for floor/ceiling assemblies: STC ratings of 50 (if tested in alaboratory) or 45 (if tested in the field*).

* The field test evaluates the dwelling’s actual construction and includes all sound

aths.

Definitions:

Sound Transmission Class rates a partition’s r esistance to airborne soundtransfer at the speech frequencies (125-4000 Hz). The higher the number, the

better the isolation.

STC Strength: Classifies an assembly’s resistance to airborne sound

transmission in a single number.

STC Weakness: This rating only assesses isolation in the speech

http://www.acoustics.com/rc.asphttp://www.acoustics.com/rc.asp


36/63

35

frequencies and provides no evaluation of the barrier’s ability to block low

frequency noise, such as the bass in music or the noise of some mechanical

equipment.

Recommended Isolation Level

An assembly rated at STC 50 will satisfy the building code requirement,

however, residents could still be subject to awareness, if not understanding,

of loud speech. It is typically argued that luxury accommodations require a

more stringent design goal (as much as 10dB better – STC 60). Regardless

of what STC is selected, all air-gaps and penetrations must be carefullycontrolled and sealed. Even a small air-gap can degrade the isolation

integrity of an assembly.

Chapter-3. Acoustical Treatments of Various Spaces

3.1 Classrooms

Tips/Considerations

Recommended reverberation time is 0.4-1.0 seconds (depending on the size o

the space).

Numerous studies demonstrate how chronic noise exposure (i.e., noise found in

the community, as well as noise to which we are voluntarily exposed)

negatively impacts education. For more information, readProgressing the

Learning Curve.

Noise from air-conditioning/heating units or other equipment on the premises

can impact the educational environment. In addition to an NC specification for

inside the classroom, specify a maximum dB level for all equipment in and

around the school.

Consider the impact of noise from nearby freeways, busy roads, train tracks and

other transportation- or industrial-related sources. Identify noise sources in the

vicinity and assess the possible impact. Based on this assessment, take the

proper steps to minimize or eliminate the potential problem.

http://www.acoustics.com/ra_learningcurve.asphttp://www.acoustics.com/ra_learningcurve.asphttp://www.acoustics.com/ra_learningcurve.asphttp://www.acoustics.com/ra_learningcurve.asphttp://www.acoustics.com/ra_learningcurve.asp


37/63

36

o Noise from adjacent classrooms can be easily transmitted into other

classrooms, particularly in an open-classroom setting. It is vital to control the

noise transfer between spaces. Keep in mind that STC ratings only address

noise isolation from 125 Hz to 4000 Hz. Low frequency sounds (below 125 Hz)

are not accounted for in an STC rating. Even if you specify a high STC rating

for the wall, it will not allow for privacy if the wall only extends to the ceiling,

or just above the ceiling. To ensure isolation, the wall must extend to, and seal

to, the deck.

Even if everything else is controlled perfectly, the space might not be usable i

the background noise (e.g. HVAC system) is too loud. To help protect your

design, the NC level should not exceed 25 to 35. When specifying NC, specify

an actual rating, such as NC 25, rather than a range, such as NC 25-30.

Although specifying a lower number will ensure minimal background noise, it

might be cost prohibitive to achieve. Be realistic about the amount of

acceptable noise and the project's budget when specifying an NC level.

3.2 Concert Hall

Goal: To create an optimal acoustic environment suitable for performanceenhancement and audibility while protecting the hearing health of the individuals using

that space.

Tips/Considerations

o

The reverberation time will depend on what type of concert is performed.

For classical or orchestral music, a higher reverberation time would be

appropriate (approximately 2 sec), for a rock concert, a lower

reverberation time would be appropriate (approximately 1 sec). Find a

happy medium, perhaps 1.5 sec. This only applies to indoor venues.

o It is vital to control the reflections from the back wall. If you don't

control them, the presentation could reflect off the back wall and "slap

back" to the presenter(s). This won't necessarily impact the audience,


38/63

37

but could be disastrous and distracting for the people on stage. Because

of this, it's usually necessary to splay or tilt the back wall to avoid slap

back. A concave back wall could compound this problem. If you can't

avoid a concave back wall, it's imperative that it be treated with

absorptive material.

o Control the reverberation time on the stage. Ideally, the reverberation

time in the stage area should be the same as in the house. Since the

stage area might have a higher ceiling than the rest of the auditorium,

more absorptive materials might be required in this area. Frequently, the

back wall of the stage, and possibly one or two of the side walls, is

treated with an acoustically absorptive material, typically black in color.

o Beware of potential noise impact to your space from exterior sources

and/or excessive HVAC noise. To help protect your design, the NC

level should not exceed 25 to 35. When specifying NC, specify an

actual rating, such as NC 30, rather than a range, such as NC 30-35.

Although specifying a lower number will ensure minimal background

noise, it might be cost prohibitive to achieve. Be realistic about the

amount of acceptable noise and the project's budget when specifying an

NC level.

o Some concert attendees have sued (and won) over experiencing hearing

loss at a concert. Beware of potentially dangerous, excessive noise

levels. Some venue operators regulate the noise levels to help alleviate

the potential noise impact on surrounding areas and on the audience.

o For outdoor venues, be sure to check on local noise ordinances. Even i

they don't exist, you should still take steps to control excessive noise

impact to the surrounding community.

Especially outdoors, be concerned about exterior noise impact on the venue. Often this

will decide the location of the site. For instance, be aware of surrounding airports

(flight paths), freeways, railroads and industrial sites.

3.3 Office


39/63

38

Tips/Considerations

o

Typical reverberation time is between 0.4 and 1 second.o Absorptive materials will most likely be necessary for the ceiling.o Even if the reverberation time is optimally controlled, reflections from

the walls can be problematic. Parallel reflective surfaces can cause anannoying condition called flutter echo or standing wave. Ideally, at leasttwo non-parallel walls should be treated with acoustically absorptivematerial. It might not be necessary to completely treat the wall as longas the critical zone (normally from 3'-7') is treated with a material thathas an NRC of at least 0.50, ideally at least 0.80.

o Draperies typically provide very little, if any, absorption.o Beware of potential noise impact to your space from exterior sources

and/or excessive HVAC noise. To help protect your design, the NClevel should not exceed 25 to 35. When specifying NC, specify anactual rating, such as NC 30, rather than a range, such as NC 25-30.Although specifying a lower number will ensure minimal backgroundnoise, it might be cost prohibitive to achieve. Be realistic about theamount of acceptable noise and the project's budget when specifying an

NC level.o Awareness of activity in adjacent spaces is typical in most offices.

However, if the transmitted speech is intelligible, it becomes far moredistracting. Additionally, confidentiality and speech privacy can become

a serious concern. Noise transfer is due to the isolation quality of a wallassembly, as well as any potential flanking paths. The isolation qualityof an assembly is largely determined by the weakest point of theassembly. Any air-gap can substantially degrade the isolation quality ofthe assembly. Even if the assembly has a high STC rating, a variety offlanking paths can allow noise transmission and speech to beunderstood between spaces. Some of the sound paths that can contributeto potential noise transfer are:

Wall Assembly Door Assembly Penetrations (outlets)

Air-Gap between wall and window mullion Flanking over the wall/through the ceiling


40/63

39

Through the ductworko If confidentiality or privacy is an issue, you need to be concerned with

the isolation quality of the wall. Even if you specify a high STC ratingfor the wall, it will not allow for privacy if the wall only extends to theceiling, or just above the ceiling. For optimal confidentiality, the wall

must extend to, and seal to, the deck. Remember, the STC rating of awall only refers to how well a section of that wall performs in alaboratory and does not necessarily indicate how well the system will

perform in the field. Specifying an NIC rating can help ensure thedesired isolation level.

Client Expectations: There is a large range of acceptable isolation levels for office

spaces. Transmitted noise that would be tolerable for some projects can be very

annoying for others. The annoyance potential is based on individual sensitivities,

confidentiality issues, and the level of privacy to which the users are accustomed. It isimportant to understand your client's needs in regard to privacy and confidentiality

expectations in order to design a space that is best suited for their individual needs.

3.4 Studio

Tips/Considerations

o Ideal sound isolation is achieved with massive construction, an airspace

and elimination of any structural connections that may transmit sound.

Unfortunately, it is very difficult to properly isolate sound when

building a studio in an existing residence, mainly because of the

common lightweight, wood frame construction and the presence of

windows (it's important to fill windows with materials comparable to

the rest of the wall). For new construction, you should specify walls

with a high STC. An appropriate STC for a home studio depends on the

specific activities taking place within the studio. Most likely, it wouldrequire an STC of 60 or more. Although STC is a good rating for speech

frequency, it does not consider the low frequency sounds.

o Achieving the optimum interior acoustic environment involves

protecting the studio from noise (noise within the space and noise

transmitted into the space) and controlling the reflections within the

space.

o Assuming all transmitted noise is controlled, the primary noise concern

is from the HVAC system (heating, ventilation and air-conditioning).


41/63

40

All mechanical equipment must be controlled to a very quiet level (NC

15-20).

o It is not necessary to cover every surface in the studio with a sound

absorbing material. This would create an acoustically "dead"

environment with too much bass sound. To create the optimum acoustic

environment, a balance of absorption and diffusion should be

considered. There are several commercially manufactured products for

both absorption and diffusion. It is recommended to consult an

acoustical expert in order to obtain specifics on particular products as

well as determine the amount and placement of such products within the

specific studio setting.

Note: Absorption and diffusion materials only help the interior acoustic environment

and do not help with isolation.

3.5 Theatre

Tips/Considerationso Recommended reverberation time is 1.0-1.5 seconds (might be higher

for some auditoriums).o Although the seating area will provide absorption, thereby reducing the

reverberation time, you will most likely need to add absorptivematerials to the other surfaces within the space.

o It is vital to control the reflections from the back wall. If you don'tcontrol them, the presentation could reflect off the back wall and "slap

back" to the presenter(s). This won't necessarily impact the audience, but could be disastrous and distracting for the people on stage. Becauseof this, it's usually necessary to treat the back wall with an absorptivematerial. A concave back wall could compound this problem. If youcan't avoid a concave back wall, it's imperative that it be treated with

absorptive material.o Splay or use irregular surfaces on the walls to avoid flutter echoes.

Parallel reflective surfaces can allow sound to "ricochet" back and forth between the surfaces. This potentially annoying co

acoustics dissertation

Documents